This invention pertains to test equipment for sensing, collecting and analyzing physical parameters associated with a conveyor oven.
Conveyor ovens are used in a variety of industries including the electronics, baking, and painting industries. Generally, conveyor ovens have multiple heating zones through which products pass. The heating zones are thermally isolated from each other by air curtains or other means. Such thermal isolation allows each zone to be maintained at a temperature that differs from other zones in the oven. A particular advantage of conveyor ovens with multiple heating zones is that the products can be heated to different temperatures at different times as they pass through the oven. In all industries that use conveyor ovens, it is important that the ovens behave consistently over time. However, after extended use, the ovens tend to degrade in performance. Some causes of this degradation include dust accumulating on oven fans and/or process bi-products, such as fluxes, accumulating on fans or blocking exhaust ports.
In the electronics industry, conveyor ovens are used to mount integrated circuits and other electronic components to printed circuit boards (PCBs). The multiple heat zones allow the PCB to be gradually raised in temperature so as to prevent thermal stress to the components and the PCB itself. Solder is placed on the PCB at predetermined points where integrated circuits are to be mounted, prior to running it through the oven. As the PCB passes through the heat zones, the solder melts, bonding the integrated circuits to the PCB. Conventionally, prior to a production run, a large number of test PCBs of the same type were passed through the oven under different heating conditions to ensure the temperature profile of the oven matched the requirements of the PCB. Each PCB was analyzed after its pass and the best setting for the oven was determined based on this analysis. This test process resulted in a significant number of test boards being scrapped due to improper heating or overuse. Other industries using conveyor ovens have experienced similar problems in setting the ovens for a production run.
To better determine optimal temperature settings and maintain existing or known settings without the need for test boards, electronic data loggers (also called data collectors) have been developed that mount to a test PCB. The test PCB has various thermocouples strategically placed thereon, which the data logger monitors. Using the data loggers, the optimal temperature of the oven can be determined. However, known data loggers have not been used to track overall oven performance, primarily because the focus of data loggers is on measuring the temperature of the product passing through the oven, not the oven itself. Additionally, known data loggers do not adequately track temperature as a function of position in the oven. Although temperature data can be collected, it is difficult to determine at what points or location in the oven the temperature data was collected.
Some companies have attempted to track oven performance by mounting a grid of thermocouples throughout the oven. If oven temperatures change over time, the user can detect these changes and take corrective action. However, the oven temperature is not the only factor in overall oven performance. The amount of air flow in the oven is also a factor in how the oven heats products. For example, many ovens (e.g., convection ovens) use forced air to heat products. Products heated in a convection oven heat more quickly than the same products heated in a standard (non-convection) oven. Consequently, reduced or increased air flow can also degrade oven performance, and temperature monitoring devices are incapable of monitoring such a degradation.
Accordingly, an object of the present invention is to provide an apparatus and method for accurately profiling oven performance. A further object is to provide such an apparatus and method that take into account both air temperature and air flow. A further object is to provide such an apparatus and method that can accurately correlate temperature data to positions within the oven. Still a further object is to provide such an apparatus and method that are easy to use and convenient.
The present invention is directed to an oven analyzing apparatus and method for profiling oven performance that accurately determine and store the physical characteristics of an oven. The stored information then can be downloaded to a computer for further analysis.
In one aspect of the present invention, the oven analyzing method and apparatus employ a pallet that moves with a conveyor through a conveyor oven. The pallet houses an electronic data logger that is coupled to multiple sensors. A first sensor is a temperature sensor that detects the ambient temperature within the oven. A second sensor is mounted within a metal mass of known thermal characteristics and detects the ovens ability to heat an object. A third sensor detects the position of the pallet within the oven. The electronic data logger stores the data received from the sensors. The stored data can then be downloaded to a computer, which can analyze the data to create an oven profile. The oven profile can be compared to other stored profiles of the same oven to detect oven degradation.
In another aspect of the invention, the pallet has a hole therethrough and the metal mass is suspended within the hole. The hole allows the metal mass to be heated by air below and above the pallet. Additionally, the metal mass is thermally isolated from the pallet so that the most accurate data concerning the oven""s ability to heat the mass is obtained.
In yet another aspect of the invention, the position sensor senses position within the oven by using a Reed switch that is actuated when the pallet passes a magnet or magnets mounted to the oven. Thus, accurate position data and conveyor speed can be calculated.
Various advantages and features of novelty which characterize the invention are particularized in the claims forming a part hereof. However, for a better understanding of the invention and its advantages, refer to the drawings and the accompanying description in which there are illustrated preferred embodiments of the invention.